Optically active amino acids, particularly optically active unnatural amino acids, are compounds useful as synthetic raw materials or intermediates for products such as agricultural chemicals and pharmaceutical products. Hence, how to efficiently produce an optically active amino acid, particularly an unnatural one, has been an industrially important problem.
Patent Document 1 discloses one method of solving this problem which involves optically resolving a racemic N-acetylamino acid as a raw material with D-aminoacylase or L-aminoacylase to give the D-form or L-form, whereby an amino acid having high optical purity is produced. With this method, however, the yield of an optically active amino acid is 50% at the highest, which means that half of a racemate goes to waste. Then, as disclosed in Patent Documents 2, 3, 4, and 5, N-acylamino acid racemase for racemizing the residual N-acetylamino acid has been proposed for use in combination with the aminoacylase in order to improve the yield. However, the resolution with use of a combination of N-acylamino acid racemase and aminoacylase has a low reactivity with an amino acid yield of only 70 to 75%. Further, the N-acyl substrate remains and thus a process for removing it is required. These problems have been impediments to practical applications.
Also, as described in Non-Patent Documents 1 and 2 and Patent Document 6, N-acylamino acid racemase has been found to have low reactivity to N-acylamino acids. In recent years, reports have been made as described in Non-Patent Documents 1 and 2 and Patent Document 6 that N-acylamino acid racemase has a higher reactivity to N-succinyl amino acids than to N-acetylamino acids, and that L-succinylase acts on N-succinyl forms of natural L-amino acids. Still, no method is known which efficiently produces an L-amino acid from an enantiomeric mixture of an N-succinyl amino acid with use of a combination of N-acylamino acid racemase and L-succinylase.
Also, an N-succinyl amino acid represented by the following formula (III) and a salt thereof, which are raw materials applicable to the present production method, have not been known:

wherein R1 represents an optionally substituted C5 to C20 alkyl group, an optionally substituted C5 to C20 alkenyl group, an optionally substituted C2 to C20 alkynyl group, an optionally substituted indanyl group, an optionally substituted naphthylmethyl group, a fluorobenzyl group, a chlorobenzyl group, or a bromobenzyl group.    Patent Document 1: JP 2006-254789 A    Patent Document 2: JP 2001-46088 A    Patent Document 3: JP 2001-314191 A    Patent Document 4: JP 2002-238581 A    Patent Document 5: JP 2007-82534 A    Patent Document 6: JP 2008-61642 A    Non-Patent Document 1: Biochemistry, 2004, Vol. 43, p. 224    Non-Patent Document 2: Biochemistry, 2006, Vol. 45, p. 4455